1. Field of the Invention
The present invention relates to a method of fabricating a semiconductor optical device for use in an optical subscriber or a wavelength division multiplexing (WDM) optical communication system and, more particularly, to a method of fabricating a semiconductor optical device that a laser diode (LD) and a semiconductor optical amplifier (SOA) are integrated.
2. Discussion of Related Art
A typical optical communication system uses a light emitting diode (LED), a Fabry-Perot laser diode (FP-LD), a distributed feedback laser diode (DFB-LD), and so on, as a light source. The LD of 1.3 μW and 1.55 μW have an optical power of about 20 mW and an oscillation start current characteristic of about 10˜20 mA. However, it is difficult to fabricate the PF-LD to have an optical power of not less than 30 mW and an oscillation start current characteristic of not more than 10 mA.
A wavelength division multiplexing-passive optical network (WDM-PON) type of optical network unit (ONU) may compose a light source for an optical subscriber in a manner of slicing a spectrum using an arrayed waveguide grating (AWG) (J. K. Park et al, “Monolithically Integrated Semiconductor LED-Amplifier for Applications as Transceivers in Fiber Access Systems”, IEEE Photonics Technology Letters, Vol. 8 No. 6, pp. 800-802, June, 1996). Characteristics of the light source required in the manner should have an optical output spectrum having a broadband width of not less than several 10 nm and an optical output intensity of not less than several mW.
From the viewpoint of the problems, the light source such as LED, FP-PD and DFB-LD used up to date have the following disadvantages.
First, while the LED may be readily fabricated and applicable to the broadband, since the intensity of output light is low, for example, several hundreds of μW or less, a system of an optical subscriber additionally requires an optical amplifier. Therefore, when the LED is used as the light source, the system becomes complicated and its price becomes high.
Second, while FP-LD and DFB-LD have a good output light of 10 mW, since they have a light output of a narrowband, optical beat interference (OBI) to an adjacent light source is generated in the subscriber system.